Are lift bags rated for the amount of positive bouyancy that they provide or for the weight of the object that they can lift? in or out of the water? Just for the fun of it, how much lift would I need to pick up and move around a small ski boat that is on the bottom? a car?
What's the deal with lift bags?
- Thread starter Bnscherm
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What is this? Seinfeld does SCUBA? 
A lift bag has to be rated for the amount of positive buoyancy they generate. If they tried to rate it for the weight of the object they can lift, they'd have to take into account density.
"Well, this bag can lift a 50 lb object provided it take up more than 1.37 cubic feet of volume. If the object takes up less than 1 cubic foot, it can only lift 34 lbs."
A lift bag has to be rated for the amount of positive buoyancy they generate. If they tried to rate it for the weight of the object they can lift, they'd have to take into account density.
"Well, this bag can lift a 50 lb object provided it take up more than 1.37 cubic feet of volume. If the object takes up less than 1 cubic foot, it can only lift 34 lbs."
DiveMaster176493
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i have moved fairly large 20 f00t boats around local quarrys with two 100lb bags 8)
Some boats, just take the concrete blocks that are holdin' it down out... no lift bag required. Others, well, it varies.Bnscherm:
***Don't mess with lifting cars "for the fun of it."***
Trust me on this.
Rick
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Bnscherm:
Well, the first thing you'll need to understand is the relationship between weight, density, and buoyancy. I would recommend that you Google Archimedes Principle and spend some time grasping the basic concepts.
Then you should get some training on how to use lift bags on smaller objects before trying for something like a boat or a car. Keep in mind that as the lift bag rises in the water column, the air inside the bag expands and the lift increases. Learning how to master using a lift bag without allowing the object being lifted to get out of control requires some practice.
If you should decide to just go ahead and start out with an object like a ski boat or car, then my advice is this ... when the lift bag(s) get away from you and start for the surface, swim away as quickly as possible ... in this case, what goes up WILL come down (assuming you're using standard open-cell lift bags) ... :11:
... Bob (Grateful Diver)
diver_paula
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uhhhhhh bnscherm,
Does this mean I may have to look for the boat in Maceday in different location next time?
Does this mean I may have to look for the boat in Maceday in different location next time?
hecker-the-wrecker
Guest
What if it's my buisiness? Sometimes we even get paid to do it. I guess after doing it for a while, i'd have to agree, don't do it "for the fun of it" it really can hit the fan quick!Rick Murchison:
Uh, you didn't ask the question...hecker-the-wrecker:What if it's my buisiness? Sometimes we even get paid to do it. I guess after doing it for a while, i'd have to agree, don't do it "for the fun of it" it really can hit the fan quick!
Rick
I guess I should have thought that question out a little bit more before asking it. The rating of positive bouyancy that a lift bag could provide is really the only way that you could make a specification. Unless, there was some standard I don't know about that measures lift based on density of an item such as lead, which could be plausible. Anyways, I don't need a science lesson in the relationship between weight, density, and buoyancy.
I have had some hands on training in the use of lift bags, but we didn't discuss the lifting capacities or what would be required. Anyway, I have no plans or interests in lifting a car or boat, I was just curious. Here's why:
http://www.scubaboard.com/showthread.php?t=97477
If the boat goes anywhere it won't be from me, but we plan on adding some attractions in the near future!
I have had some hands on training in the use of lift bags, but we didn't discuss the lifting capacities or what would be required. Anyway, I have no plans or interests in lifting a car or boat, I was just curious. Here's why:
http://www.scubaboard.com/showthread.php?t=97477
If the boat goes anywhere it won't be from me, but we plan on adding some attractions in the near future!
captainoncove
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lift bag experiance needed to lift a 30000 lb aluminum boat from 140 feet deep in ocean. vessle is sitting in up right position, just like being at the dock.except the outriggers and divers are down. commercial fishing vessel.
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